The lawsuit asks for a court order declaring the charter amendment void.

It joins 10 previous lawsuits and administrative charges filed by individuals and unions, including the police association itself, to challenge the measure on various grounds.

Adams said that while the police union’s earlier lawsuit challenges the substance of Measure B by claiming that it violates vested pension rights, the new lawsuit disputes the process by which it was put on the ballot.

“It’s a procedural lawsuit, but it could invalidate the whole measure,” Adams said.

Mayor Chuck Reed, who championed Measure B, said in a statement that the city “spent hundreds of hours negotiating with its employee unions over the Measure B pension reforms.”

“I am confident that the courts will agree that the city bargained in good faith and fulfilled all of its meet-and-confer obligations,” Reed said.

The charter amendment, enacted by nearly 70 percent of city voters, gives current employees the option of taking a lower pension or paying more for their current plan, and requires new employees to pay 50 percent of pension costs.

The police union’s new lawsuit required the permission of the office of state Attorney General Kamala Harris before it could be filed. The office gave that permission two weeks ago.

Harris spokeswoman Lynda Gledhill said the go-ahead doesn’t mean that Harris endorses the lawsuit, but merely that the attorney general agreed that the issue should go before a judge.

Of the other 10 lawsuits and complaints, six lawsuits that challenge the substance of the charter amendment, including the police union’s 2012 lawsuit, are due to go to trial together before Santa Clara Superior Court Judge Patricia Lucas on July 22, according to Adams and City Attorney Rick Doyle.

Four other cases filed by groups including engineers’ and firefighters’ unions are based on procedural claims of failure to bargain, similar to the claims in the new police union lawsuit.

Those cases were filed as charges of unfair labor practices with the state Public Employment Relations Board, which has jurisdiction over most government worker unions, but not police unions, in such matters.

In March, PERB accepted those charges as administrative complaints.

PERB Deputy General Counsel Wendy Ross said the complaints were scheduled for an informal settlement conference on July 9. If there is no settlement, the cases will then be heard by an administrative law judge within two or three months, she said. That judge’s decision can be appealed to the board and then to a state appeals court in San Jose.

Because PERB doesn’t have jurisdiction over unfair labor charges lodged by public safety unions, the Police Officers’ Association took its case to Superior Court after getting Harris’s permission.

After Harris’s office issued its formal opinion on April 15 allowing the lawsuit to be filed, “we expected it,” said Doyle.

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